This invention relates generally to battery chargers, and more particularly to battery chargers having indicators for indicating, in a charging operation, that a secondary cell, or battery of secondary cells, has reached full charge.
After full charge is achieved and charging continues beyond the full charge point, it has been observed that in certain cells there results a rise in temperature of the fully-charged battery or cell. In the present invention, this rise in temperature is employed to provide the desired full charge indication by virtue of a relative change in a perceivable parameter of the heat sensitive indicator.
Thus, the battery charger with indicator according to the present invention is operable with secondary cells, notably sealed cells, which become heated when, after being fully charged, they are subjected to further charging current. Therefore, as used hereinafter, the term "cell or battery" shall refer to sealed cells or like cells which are so heated.
Battery chargers adapted to indicate that a battery or cell has reached full charge in a charging operation are highly useful, since without indicators of any type it is often difficult to ascertain in simple fashion whether and when a battery or cell has reached full charge. This is particularly true of nickel-cadmium cells because there is no ready way to determine state-of-charge such as, for example, by measuring open circuit voltage as can be used for measuring the charge in lead-acid cells. Therefore, it may be necessary to test or measure the cell charge to ensure that full charge has been achieved. Thus, much effort and electrical energy would have to be wasted either in measuring the actual charge level of the battery, or in permitting the battery or cell to remain in the charging operation for a time longer than the minimum necessary to fully charge that particular cell.
Accordingly, it is an object of this invention to provide a battery charger with indicating device for providing charging current and indicating when each cell or battery therein has reached full charge.
It is also an object of this invention to provide a battery charger with indicating device for indicating that cells or batteries therein have reached full charge, the indicator being relatively compact, easily readable, and relatively inexpensive to manufacture.
It is a further object of this invention to provide a battery charger with full-charge indicator which obviates the expense of adhering an indicator to each cell or battery.
Objects and advantages of the invention are set forth in part above and in part below. In addition, these and other objects and advantages of the invention will become apparent herefrom or may be appreciated by practice with the invention, the same being realized and attained by the instrumentalities, combinations, and methodologies pointed out in the appended claims. Accordingly, the invention resides in the novel parts, arrangements, combinations, steps, methods, and improvements herein shown and described.